<template>
  <div class="spec-preview">
    <!-- 遮罩板底下的大图 -->
    <img :src="imgObj.imgUrl" />
    <!--  -->
    <div class="event" @mousemove="changeMove"></div>
    <!-- 右侧的大图 -->
    <div class="big">
      <img :src="imgObj.imgUrl" ref="big" />
    </div>
    <!--移动的遮罩层 -->
    <div class="mask" ref="mask"></div>
  </div>
</template>

<script>
export default {
  name: "Zoom",
  props: ["imageList"],
  data() {
    return {
      currentIndex: 0,
    };
  },
  computed:{
    imgObj(){
      return this.imageList[this.currentIndex]||{}
    }
  },
  mounted(){
    this.$bus.$on('changeIndex', (index)=>{
      this.currentIndex = index
    })
  },

  methods: {
    changeMove(event) {
      let mask = this.$refs.mask;
      let big = this.$refs.big;
      //计算出移动的时候遮罩层l、t
      let l = event.offsetX - mask.offsetWidth / 2;
      let t = event.offsetY - mask.offsetHeight / 2;
      //约束left|top数值
      if (l <= 0) l = 0;
      if (l >= mask.offsetWidth) l = mask.offsetWidth;
      if (t <= 0) t = 0;
      if (t >= mask.offsetHeight) t = mask.offsetHeight;
      //动态修改遮罩层的l、t
      mask.style.left = l + "px";
      mask.style.top = t + "px";
      //修改大图的left|top
      big.style.left = -2 * l + "px";
      big.style.top = -2 * t + "px";
    }
  }
};
</script>

<style lang="less" scoped>
.spec-preview {
  position: relative;
  width: 400px;
  height: 400px;
  border: 1px solid #ccc;

  img {
    width: 100%;
    height: 100%;
  }

  .event {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 998;
  }

  .mask {
    width: 50%;
    height: 50%;
    background-color: rgba(0, 255, 0, 0.3);
    position: absolute;
    left: 0;
    top: 0;
    display: none;
  }

  .big {
    width: 100%;
    height: 100%;
    position: absolute;
    top: -1px;
    left: 100%;
    border: 1px solid #aaa;
    overflow: hidden;
    z-index: 998;
    display: none;
    background: white;

    img {
      width: 200%;
      max-width: 200%;
      height: 200%;
      position: absolute;
      left: 0;
      top: 0;
    }
  }

  .event:hover ~ .mask,
  .event:hover ~ .big {
    display: block;
  }
}
</style>